Methods, materials, and equipment useful in chemical-mechanical polishing (CMP) or planarizing of a substrate are highly varied and are available for processing a wide range of substrates having different surfaces and end applications. Substrates that are processed by CMP methods include optical products and semiconductor substrates at any of various stages of fabrication. A wide range of CMP apparatuses, slurries, polishing pads, and methods are well-known and more are being continually developed.
Polishing compositions (also known as polishing slurries, CMP slurries, and CMP compositions) are designed to process (e.g., polish, planarize) a surface of a semiconductor substrate. Some such surfaces contain a metal such as tungsten. A polishing slurry may contain chemical ingredients that are selected specifically for processing a certain type of substrate, such as for polishing a tungsten-containing surface as opposed to surfaces that do not contain a metal or that contain a metal different from tungsten. Examples of such chemical ingredients include chemical catalysts, inhibitors, chelating agents, surfactants, oxidants, among others; each of these may be selected to improve desired processing of a metal or non-metal component of a substrate surface. In addition, the polishing composition may contain abrasive particles suspended in an aqueous medium. The type of abrasive particles may also be selected based on the type of substrate being processed. Certain types of abrasive particles may be useful in polishing a tungsten-containing substrate surface but may not be useful for processing other CMP substrate surfaces.
Methods of polishing tungsten-containing substrates have become important for advanced nodes of semiconductor processing. In a conventional tungsten-polishing operation, a substrate (wafer) to be polished is mounted on a carrier (polishing head), which is in turn mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus (polishing tool). The carrier assembly provides a controllable pressure to the substrate, pressing the substrate against the polishing pad. The substrate and pad are moved relative to one another by an external driving force. The relative motion of the substrate and pad abrades and removes material from the surface of the substrate, thereby polishing the substrate. Polishing and removal of material may be based on the combined effects of the chemical activity of the polishing composition (e.g., by catalyst, oxidizing agent, etc., present in the polishing slurry), and the mechanical activity of the abrasive particles suspended in the polishing composition.
Examples of steps of semiconductor processing that involve tungsten at a surface of a substrate include preparing tungsten “plug” and “interconnect” structures within a dielectric layer. By these methods, tungsten is deposited over a dielectric layer that includes openings, with the tungsten flowing into the openings to fill the openings. Excess tungsten will also be deposited over the dielectric layer and must be removed. The tungsten is removed by CMP polishing to leave behind the tungsten plugs and tungsten interconnects filled into the initial openings of the dielectric layer, as components of a planarized substrate surface.
As semiconductor device feature sizes continue to shrink, meeting local and global planarity requirements becomes more difficult in CMP operations (e.g., in tungsten polishing operations). Array erosion (also referred to as oxide erosion), plug and line recessing, and tungsten etching defects are known to compromise planarity and overall device integrity. For example, excessive array erosion may lead to difficulties in subsequent lithography steps as well as electrical contact problems that can degrade electrical performance. Tungsten etching, tungsten corrosion, and plug and line recessing may also degrade electrical performance or even cause device failure. The polishing process is desirably effective to remove an amount of tungsten without producing unacceptable erosion or other undesired topography effects at the substrate surface. Also desired are a low level of scratching and a low amount of residue left at the polished surface.
While maintaining or improving performance levels, the semiconductor industry is always subject to downward pricing pressure. High processing throughput is required to achieve desired economics. High throughput can be achieved with high removal rates of tungsten or other materials. Downward pricing pressure applies also to CMP consumables themselves, such as slurries, meaning that a lower cost slurry or a slurry that can be used with lower operational costs or cost of ownership will also be economically advantageous. Slurries that include less water (and, e.g., higher concentrations of abrasive particles) during storage, transportation, or use, can have a significant positive impact on cost of ownership.
In view of the above, there is ongoing need in the semiconductor processing industry for a CMP slurry useful for polishing a tungsten-containing substrate, that provides improvements in one or more of: planarity of a polished surface, reduced defects in a polished surface (e.g., reduced scratching and reduced residue), reduced particle size growth during processing (increased size of abrasive particles can correspond to high defectivity), high throughput (e.g., due to useful or high removal rates for tungsten, oxide (e.g., TEOS), or both), and reduced overall cost (such as by improved concentratability).